Impacts of surface roughness and loading conditions on cyclic direct shear behaviors of an artificial frozen silt–structure interface Lianzhen Zhao a,b , Ping Yang b , J.G. Wang c,d, ⁎, Lai-Chang Zhang a a School of Engineering, Edith Cowan University, 270 Joondalup Drive, Joondalup, Perth, WA 6027, Australia b Department of Civil Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China c School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China d State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining and Technology, Xuzhou 221116, China abstract article info Article history: Received 23 March 2014 Accepted 24 July 2014 Available online 31 July 2014 Keywords: Frozen soil–structure interface Roughness Loading condition Cyclic direct shear behavior Maximum shear stress Normal displacement The mechanical properties of the interface between frozen soils and structures are of importance in practice to the design and safety assessment of a frozen soil–structure system in permafrost regions and artificial frozen soils. In practice, frozen soil–structure interfaces are subjected to complex loading conditions and the surface roughness of a structure varies in a certain range. Their impacts on the cyclic direct shear behaviors of an artificial frozen soil–structure interface are interesting but unsolved issues. In this study, a series of direct shear tests were conducted to explore these impacts through characterizing the cyclic direct shear behaviors of an artificial frozen silt–structure interface. Particularly, these direct shear tests, which include monotonic shear tests, constant nor- mal stress tests, and constant normal stiffness tests, were carried out under circumstances of different frozen temperatures and/or interface roughness. Shear stresses and normal stresses (or normal displacements) were measured under cyclic loading. These experiments revealed the following mechanical behaviors of the artificial frozen interface: (1) in monotonic shear tests, maximum shear stress is observed at the shear displacement of approximately 0.7 mm. (2) The order of the magnitude of final shear stress from high to low is from constant nor- mal stress tests, monotonic shear tests, constant normal stiffness tests, constant normal stress tests under rising temperature condition, and constant normal stiffness tests under rising temperature condition. (3) Both rough- ness and frozen temperature at shear have vital impacts not only on the maximum shear stress but also on the final shear stress. The roughness has much stronger impacts on the maximum shear stress than on the final shear stress. A critical roughness is observed from the relationship between the maximum shear stress and roughness. (4) Roughness, loading condition and cyclic loading time are three key factors to normal displace- ments. Both maximum dilation and final normal displacement increase with roughness increasing. The maxi- mum dilation firstly increases with roughness increasing and then decreases from a certain roughness of about 0.8 mm. However, the loading conditions have slightly different impacts on the final normal displacement from the maximum dilation. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Massive frozen soil–structure interfaces exist between building foundations and their surrounding frozen soils in permafrost regions and artificial frozen grounds. The interfaces are very important elements to the safety in freeways, foundations, tunnels, dams, embank- ments, oil pipelines, and substructures (Dan et al., 2014; Kang et al., 2013; Lai et al., 2012; Z. Liu et al., 2014; Wagner, 2013; Wen et al., 2010). During project operations, these frozen soil–structure interfaces are vulnerable to cyclic loadings such as seismic and wind loads therefore become one of the most important elements which affect the safety and sustainability of a building (Sukhorukov and Marchenko, 2014). The mechanical properties of unfrozen soil–structure interfaces and frozen soils alone have been widely investigated (Cui et al., 2014; Ma et al., 1999; Rist et al., 2012; Zhu et al., 2010, 2011), however, limited publications have focused on the mechanical behaviors of a frozen soil– structure interface with a range of roughness under different loading conditions (J. Liu et al., 2014; Zhao et al., 2014). As such, it is necessary to investigate the impacts of surface roughness and loading conditions on the mechanical behaviors of a soil–structure interface, particularly including cyclic direct shear behaviors. The mechanical properties of soil–structure interfaces are signifi- cantly impacted by two important factors: the roughness of interface (or the roughness of a structure surface) and loading conditions. For example, DeJong and Westgate (2009) conducted a series of monotonic Cold Regions Science and Technology 106–107 (2014) 183–193 ⁎ Corresponding author at: School of Mechanical and Chemical Engineering, The University of Western Australia, Crawley, Perth, WA 6009, Australia. Tel.: +61 424455936; fax: +61 864881024. E-mail addresses: yangping@njfu.com.cn (P. Yang), nuswjg@yahoo.com (J.G. Wang). http://dx.doi.org/10.1016/j.coldregions.2014.07.009 0165-232X/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Cold Regions Science and Technology journal homepage: www.elsevier.com/locate/coldregions